In recent years evidence has accumulated showing that not only biogenic amines but also their metabolites, the biogenic aldehydes and biogenic alcohols, may exert biological activity. Drugs acting on the central nervous system, such as alcohol and/or acetaldehyde, phenobarbital and chloral hydrate interfere with the metabolism of biogenic aldehydes. The objective of this research is to investigate the enzyme systems common to the metabolism of alcohol, acetaldehyde and metabolites derived from biogenic amines. In human and rat brain or liver a heterogeneity is observed for alcohol dehydrogenase, aldehyde reductase and aldehyde dehydrogenase. An understanding of the enzymatic mechanisms involved should provide a basis to affect the metabolism of biogenic aldehydes and alcohols as putative neuromodulators in vivo. Furthermore, the study should improve our understanding of the mechanisms underlying acute and longterm effects of drugs such as alcohol.